<template>
  <ul class="list" >
    <li class="item"
        v-for="item of letters" 
        :key="item"
        :ref="item"
        @touchstart.prevent="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        @click="handleLetterClick"
      >
        {{item}}
    </li>
  </ul>
</template>

<script>
export default {
		name: 'CityAlphabet',
    props: {
      cities: Object
    },
    computed: {
      letters () {
        const letters = []
        for (let i in this.cities) {
          letters.push(i)
        }
        return letters

      }
    },
    data () {
      return {
        touchStatus: false,
        startY: 0,
        timer: null
      }
    },
    updated () {
      this.startY = this.$refs['A'][0].offsetTop
    },
    methods: {
      handleLetterClick (e) {
        this.$emit('change',e.target.innerText)
      },
      handleTouchStart () {
        this.touchStatus = true
      },
      handleTouchMove (e) { 
        if (this.touchStatus) {
          if (this.timer) {
            clearTimeout(this.timer)
          }
          this.timer = setTimeout(() => {
            const touchY = e.touches[0].clientY - 79
            const index = Math.floor((touchY - this.startY) / 20)
            if (index >= 0 && index < this.letters.length) {
              this.$emit('change', this.letters[index])
            }
          },16)         
        }
      },
      handleTouchEnd () {
        this.touchStatus = false
      }
    }
	}
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl'
.list
  display: flex
  flex-direction: column
  justify-content: center
  position: absolute
  top: 1.58rem
  right: 0
  bottom: 0
  width: .4rem
  .item
    line-height: .4rem
    text-align: center
    color: $bgColor
</style>